Any serious debt-reduction plan has to include revenue and defense cuts. But no serious one can exclude entitlements. …

With Republicans in control of the House and holding 45 votes in the Senate, this is basic political realism. It’s also fiscal realism, as the most recent Congressional Budget Office review of the long-term budget outlook, published in June, explained. Spending on retirement income and health care is headed inexorably higher as the population ages. In 2012, Social Security, Medicare and Medicaid accounted for 10.4 percent of gross domestic product (GDP). All other non-interest federal outlays, defense included, totaled 11.6 percent of GDP. If present policies and population trends continue, the three entitlement programs would grow to 12.9 percent of GDP by 2022, while all other spending would shrink by 4 percentage points as a share of GDP.

It’s eminently possible to rein in entitlements without imposing hardship on the neediest. A reform Mr. Obama considered during the 2011 talks — gradually raising the Medicare eligibility age from 65 to 67 — would save roughly $150 billion over 10 years, according to the Congressional Budget Office, while aligning the program with modern life expectancy. With health-care reform now entrenched, those younger than 67 need not fear going uninsured.